Physical Description

Fangtooths have shortened, deep bodies with characteristically large mouth lined with sharp, fang-like teeth from which the species gained its common name. Relative to body size, they have the largest teeth of any marine species, with one of their most prominent features being a pair of long anterior fangs in the upper jaw. The length of their teeth prohibits them from completely closing their mouth. They are uniformly dark brown to black in color, and most of their body is covered with thin, prickly scales and spines. Lateral lines are seen as distinctly open grooves on either side of the body, and are partially covered with scales at various intervals. They typically have between 17 and 20 dorsal soft rays, seven to nine anal soft rays, and 28 vertebrae. They lack both dorsal and anal spines. Swim bladders are present, and relative to most other deep-sea fish, fangtooths have powerful muscles. Fangtooths are sexually dimorphic as adult females tend to be larger than their male counterparts.

Juvenile and adult fangtooths exhibit vast morphological differences. Juveniles have a long cephalic and preopercular spine. Their eyes are large, but their teeth are small and are not found on the palatine or the vomer. However, they have multiserial teeth on their premaxilaries. Juvenile gill rakers are described as long and slender. They have long head spines and are more lightly colored than adults. In contrast, adults do not have cephalic or preopercular spines. Their eyes are comparatively small, and their gill-rakers are tooth-like and are found in groups with bony bases. Juveniles begin to look like adults when they reach approximately 8 cm in length, and adults generally grow to a length of 17 cm.

Anoplogaster cornuta is stenothermic and is adapted to temperatures between 4°C and 6ºC. Due to the depths at which adults are typically found, various mechanisms have been proposed for its survival under high hydrostatic pressure in the oxygen minimum layers of the ocean. One study found that there was a significant positive relationship between oxygen consumption rates and critical oxygen tension, leading to at least two possible explanations. One is that A. cornuta only occasionally visits the oxygen minimum zone and that it is capable of sustained oxygen debt during these visits. Alternatively, these organisms might only engage in anaerobic metabolism in the oxygen minimum zone.